Method for producing β-hydroxy amino acid and enzyme used therefor

ABSTRACT

A method for producing β-hydroxy amino acid and its optically-active isomer is provided. The β-hydroxy amino acid is produced by reacting a predetermined D-α-amino acid and 5,10-methylene tetrahydrofolic acid in the presence of an enzyme derived from a microorganism belonging to the genera  Paracoccus, Aminobacter , or  Ensifer.

This application claims priority under 35 U.S.C. §119(a) to JP 2005-148659, filed in Japan on May 20, 2005, the entirety of which is incorporated by reference. The Sequence Listing on Compact Disk filed herewith is also hereby incorporated by reference in its entirety (File Name: US-288 Seq List; File Size: 32 KB; Date Created: May 22, 2006).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for producing β-hydroxy amino acid and in particular, to a method for producing the β-hydroxy amino acid using a novel enzyme.

2. Brief Description of the Related Art

Amino acids such as β-hydroxy amino acid and amino acids having optical activity at an α-position are expected to be used as intermediates for pharmaceuticals. Examples of methods for producing optically-active α-alkyl serine derivatives which are optically-active amino acid derivatives having two different substituents at the α-position, and salts thereof, include the following methods:

1) asymmetric alkylation of an optically-active oxazolidine compound obtained from the optically-active serine derivative and pivalaldehyde (Seebach et al., Helvetica Chimica Acta, 1987, 70:1194-1216);

2) asymmetric aldol reaction of α-isocyano carboxylic acid ester and paraformaldehyde with an optically-active metal catalyst (Yoshihiko et al., Tetrahedron Letters, 1988, 29:235-238);

3) asymmetric alkylation of optically-active β-lactam compounds obtained from an optically active oxazolidine chromium carbene complex and an oxazine compound (Colson et al., Journal of Organic Chemistry, 1993, 58:5918-5924);

4) asymmetric ring-opening reaction of an optically-active aziridine compound (Wipf et al., Tetrahedron Letters, 1995, 36:3639-3642)

5) asymmetric alkylation of an optically-active pyrazinone compound obtained from an optically-active valine derivative and an optically-active alanine derivative (Najera et al., European Journal of Organic Chemistry, 2000, 2809-2820); and

6) Sharpless asymmetric dihydroxylation of a 2-methyl-2-propenoic acid derivative followed by introduction of a resulting optically-active diol compound into an optically-active azido compound for reduction (Avenoza et al., Tetrahedron Asymmetry, 2001, 12:949-957).

α-Methyl-L-serine is one of the promising substances which may be used as an intermediate of a medicament. In one of the known methods for producing α-methyl-L-serine by means of an enzymatic reaction, D-alanine and 5,10-methylenetetrahydrofolic acid are used as the materials, and 2-methyl serine hydroxymethyl transferase (EC 2.1.2.7) is used as the enzyme. However, this method utilizes an enzyme derived from a microorganism belonging to genus Pseudomonas, and requires the addition of expensive α-methyl-serine in order to produce an enzyme in a cultivation medium (Wilson et al., J. Biol. Chem 237:3171-3179). In addition, utilizing the enzyme derived from the microorganism belonging to genus Pseudomonas, α-methyl-L-serine is obtained from 4 mmol of material (D-Ala) with a yield of as low as 11%, which does not satisfy the requirements for practical use.

SUMMARY OF THE INVENTION

As mentioned above, many studies have been conducted on a wide variety of methods for producing optically-active amino acids. Nevertheless, a simpler, more effective, and cost-efficient method for producing a variety of optically-active amino acids and β-hydroxy amino acid is desirable. The object of the present invention is to provide a new simpler method for producing β-hydroxy amino acid and optically-active β-hydroxy amino acid, as well as an enzyme which may be used in the method.

A novel method has been developed for producing a β-hydroxy amino acid, and a new protein has been found which catalyzes the reaction in a reaction system where 5,10-methylenetetrahydrofolic acid and/or a predetermined aldehyde are involved, and using a D-amino acid as a starting material. It has also been determined that this protein can be used to conveniently produce a β-hydroxy amino acid. In addition, it has also been determined that production with this protein results in selective production of an L-amino acid if the product is an amino acid having optical activity. The present invention provides a method for producing a β-hydroxy amino acid and an enzyme used in the method, as mentioned below.

It is an object of the present invention to provide a method for producing a β-hydroxy amino acid of formula (III):

comprising reacting a D-α-amino acid of formula (I):

with 5,10-methylenetetrahydrofolic acid and/or an aldehyde of formula (II):

in the presence of an enzyme isolated from a microorganism belonging to a genus selected from the group consisting of Paracoccus, Aminobacter, and Ensifer, and

wherein R¹ and R² are each selected from the group consisting of an alkyl group with 1 to 6 carbon atoms, an aryl group with 6 to 14 carbon atoms, a cycloalkyl group with 3 to 10 carbon atoms, an aralkyl group with 7 to 19 carbon atoms, an alkoxyalkyl group with 2 to 11 carbon atoms, a group identical to any of the aforementioned groups except for containing a hetero atom in the carbon skeleton thereof, and a group identical to any of the aforementioned groups except for containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and

wherein R³ is selected from the group consisting of hydrogen, an alkyl group with 1 to 6 carbon atoms, an aryl group with 6 to 14 carbon atoms, a cycloalkyl group with 3 to 10 carbon atoms, an aralkyl group with 7 to 19 carbon atoms, an alkoxyalkyl group with 2 to 11 carbon atoms, a group identical to any of the aforementioned groups except for containing a hetero atom in the carbon skeleton thereof, and a group identical to any of the aforementioned groups except for containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and

wherein R¹, R², and R³ may be either linear or branched, and may have a substituent.

It is a further object of the present invention to provide the method described above, wherein said D-α-amino acid is D-α-alanine and said β-hydroxy amino acid is α-methyl-L-serine.

It is even a further object of the present invention to provide a method for producing β-hydroxy amino acid of formula (III):

comprising reacting a D-α-amino acid of formula (I):

with 5,10-methylenetetrahydrofolic acid and/or an aldehyde of formula (II):

in the presence of a protein selected from the group consisting of:

-   (A) a protein comprising the amino acid sequence of SEQ ID NO: 5; -   (B) a variant protein of the amino acid sequence of SEQ ID NO: 5,     which is able to catalyze the reaction to produce the β-hydroxy     amino acid of formula (III); -   (C) a protein comprising the amino acid sequence of SEQ ID NO: 11; -   (D) a variant protein of the amino acid sequence of SEQ ID NO: 11,     which is able to catalyze the reaction to produce the β-hydroxy     amino acid of formula (III); -   (E) a protein comprising the amino acid sequence of SEQ ID NO: 16;     and -   (F) a variant protein of the amino acid sequence of SEQ ID NO: 16,     which is able to catalyze the reaction to produce the β-hydroxy     amino acid of formula (III), and

wherein, R¹ and R² are each selected from the group consisting of an alkyl group with 1 to 6 carbon atoms, an aryl group with 6 to 14 carbon atoms, a cycloalkyl group with 3 to 10 carbon atoms, an aralkyl group with 7 to 19 carbon atoms, an alkoxyalkyl group with 2 to 11 carbon atoms, a group identical to any of the aforementioned groups except for containing a hetero atom in the carbon skeleton thereof, and a group identical to any of the aforementioned groups except for containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and

wherein R³ is selected from the group consisting of hydrogen, an alkyl group with 1 to 6 carbon atoms, an aryl group with 6 to 14 carbon atoms, a cycloalkyl group with 3 to 10 carbon atoms, an aralkyl group with 7 to 19 carbon atoms, an alkoxyalkyl group with 2 to 11 carbon atoms, a group identical to any of the aforementioned groups except for containing a hetero atom in the carbon skeleton thereof, and a group identical to any of the aforementioned groups except for containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and

wherein R¹, R², and R³ may be either linear or branched, and may have a substituent.

It is even a further object of the present invention to provide the method as described above, wherein said D-α-amino acid is D-α-alanine and said β-hydroxy amino acid is α-methyl-L-serine.

It is even a further object of the present invention to provide a protein isolated from a microorganism belonging to a genus selected from the group consisting of Paracoccus, Aminobacter, and Ensifer, and wherein said protein is able to catalyze the reaction of a D-α-amino acid of formula (I):

with 5,10-methylenetetrahydrofolic acid and/or an aldehyde of formula (II):

to produce a β-hydroxy amino acid of formula (III):

wherein R¹ and R² are each selected from the group consisting of an alkyl group with 1 to 6 carbon atoms, an aryl group with 6 to 14 carbon atoms, a cycloalkyl group with 3 to 10 carbon atoms, an aralkyl group with 7 to 19 carbon atoms, an alkoxyalkyl group with 2 to 11 carbon atoms, a group identical to any of the aforementioned groups except for containing a hetero atom in the carbon skeleton thereof, and a group identical to any of the aforementioned groups except for containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and

wherein R³ is selected from the group consisting of hydrogen, an alkyl group with 1 to 6 carbon atoms, an aryl group with 6 to 14 carbon atoms, a cycloalkyl group with 3 to 10 carbon atoms, an aralkyl group with 7 to 19 carbon atoms, an alkoxyalkyl group with 2 to 11 carbon atoms, a group identical to any of the aforementioned groups except for containing a hetero atom in the carbon skeleton thereof, and a group identical to any of the aforementioned groups except for containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and

wherein R¹, R², and R³ may be either linear or branched, and may have a substituent.

It is even a further object of the present invention to provide a protein which is able to catalyze the reaction of a D-α-amino acid of formula (I):

with 5,10-methylenetetrahydrofolic acid and/or an aldehyde of formula (II):

to produce a β-hydroxy amino acid of formula (III):

wherein R¹ and R² are each selected from the group consisting of an alkyl group with 1 to 6 carbon atoms, an aryl group with 6 to 14 carbon atoms, a cycloalkyl group with 3 to 10 carbon atoms, an aralkyl group with 7 to 19 carbon atoms, an alkoxyalkyl group with 2 to 11 carbon atoms, a group identical to any of the aforementioned groups except for containing a hetero atom in the carbon skeleton thereof, and a group identical to any of the aforementioned groups except for containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and

wherein R³ is selected from the group consisting of hydrogen, an alkyl group with 1 to 6 carbon atoms, an aryl group with 6 to 14 carbon atoms, a cycloalkyl group with 3 to 10 carbon atoms, an aralkyl group with 7 to 19 carbon atoms, an alkoxyalkyl group with 2 to 11 carbon atoms, a group identical to any of the aforementioned groups except for containing a hetero atom in the carbon skeleton thereof, and a group identical to any of the aforementioned groups except for containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and

wherein R¹, R², and R³ may be either linear or branched, and may have a substituent, and

wherein said protein is selected from the group consisting of:

-   (A) a protein comprising the amino acid sequence of SEQ ID NO: 5, or     a variant protein thereof; -   (B) a protein comprising the amino acid sequence of SEQ ID NO: 11,     or a variant protein thereof; -   (C) a protein comprising the amino acid sequence of SEQ ID NO: 16,     or a variant protein thereof.

It is even a further object of the present invention to provide a polynucleotide encoding the protein as described above.

It is even a further object of the present invention to provide a polynucleotide selected from the group consisting of:

-   (a) a polynucleotide comprising the nucleotide sequence of SEQ ID     NO: 4; -   (b) a polynucleotide which hybridizes with a nucleotide sequence     complementary to that of SEQ ID NO: 4 under stringent conditions,     and which encodes a protein which is able to catalyze the reaction     of D-α-amino acid of formula (I) with 5,10-methylenetetrahydrofolic     acid and/or an aldehyde of formula (II) to produce β-hydroxy amino     acid of formula (III); -   (c) a polynucleotide comprising the nucleotide sequence of SEQ ID     NO: 10; -   (d) a polynucleotide which hybridizes with a nucleotide sequence     complementary to that of SEQ ID NO: 10 under stringent conditions,     and which encodes a protein which is able to catalyze the reaction     of D-α-amino acid of formula (I) with 5,10-methylenetetrahydrofolic     acid and/or an aldehyde of formula (II) to produce β-hydroxy amino     acid of formula (III); -   (e) a polynucleotide comprising the nucleotide sequence of SEQ ID     NO: 15; -   (f) a polynucleotide which hybridizes with a nucleotide sequence     complementary to that of SEQ ID NO: 15 under stringent conditions,     and which encodes a protein which is able to catalyze the reaction     of D-α-amino acid of formula (I) with 5,10-methylenetetrahydrofolic     acid and/or an aldehyde of formula (II) to produce β-hydroxy amino     acid of formula (III); and     wherein formula (I) is:

wherein formula (II) is:

wherein formula (III) is:

wherein, R¹ and R² are each selected from the group consisting of an alkyl group with 1 to 6 carbon atoms, an aryl group with 6 to 14 carbon atoms, a cycloalkyl group with 3 to 10 carbon atoms, an aralkyl group with 7 to 19 carbon atoms, an alkoxyalkyl group with 2 to 11 carbon atoms, a group identical to any of the aforementioned groups except for containing a hetero atom in the carbon skeleton thereof, and a group identical to any of the aforementioned groups except for containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and

wherein R³ is selected from the group consisting of hydrogen, an alkyl group with 1 to 6 carbon atoms, an aryl group with 6 to 14 carbon atoms, a cycloalkyl group with 3 to 10 carbon atoms, an aralkyl group with 7 to 19 carbon atoms, an alkoxyalkyl group with 2 to 11 carbon atoms, a group identical with any of the aforementioned groups except for containing a hetero atom in the carbon skeleton thereof, and a group identical with any of the aforementioned groups except for containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, and

wherein R¹, R², and R³ may be either linear or branched and may have a substituent.

It is even a further object of the present invention to provide a recombinant polynucleotide having the polynucleotide as described above incorporated therein.

It is even a further object of the present invention to provide a transformant having the polynucleotide as described above incorporated therein.

It is even a further object of the present invention to provide a recombinant polynucleotide having the polynucleotide as described above incorporated therein.

It is even a further object of the present invention to provide a transformant having the polynucleotide according to claim 11 incorporated therein.

It is even a further object of the present invention to provide the method as described above, wherein said variant protein of the amino acid sequence of SEQ ID NO. 5 is 90% homologous to SEQ ID NO. 5, said variant protein of the amino acid sequence of SEQ ID NO. 11 is 90% homologous to SEQ ID NO. 11, and said variant protein of the amino acid sequence of SEQ ID NO. 16 is 90% homologous to SEQ ID NO. 16.

It is even a further object of the present invention to provide the protein as described above, wherein said variant protein in (A) is 90% homologous to SEQ ID NO. 5, said variant protein of (B) is 90% homologous to SEQ ID NO. 11, and said variant protein of (C) is 90% homologous to SEQ ID NO. 16.

The present invention allows a β-hydroxy amino acid to be produced by simple procedures.

In the production of an optically active β-hydroxy amino acids, the present invention allows selective production of an L-amino acid. Thus, the present invention provides an efficient method for producing the L-amino acid. Furthermore, the present invention may achieve the production of the recombinant and transformant of the novel enzyme, leading to low-cost, large-scale production of amino acids.

The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of the presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scheme showing the reaction system according to one embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The embodiments according to the present invention will be described hereinbelow with reference to the best mode of carrying out the invention.

It should be noted that various types of genetic engineering approaches are described in many standard experimental manuals, such as Molecular Cloning: A Laboratory Manual, 3^(rd) edition, Cold Spring Harbor press (2001 Jan. 15), Saibo Kogaku Handbook (Cellular Engineering Handbook), Toshio KUROKI et al., Yodosya (1992), and Shin Idenshi Kogaku Handbook (New Gene Engineering Handbook), 3^(rd) edition, Matsumura et al., Yodosya (1999), and by reference to these manuals, a person skilled in the art may easily use these approaches.

In the specification, SEQ ID NOs. refers to the sequence numbers in a sequence listing unless otherwise stated. In the specification, an enzyme is a protein which is able to catalyze a chemical reaction.

In the method of the present invention for producing the β-hydroxy amino acid, a D-α-amino acid of formula (I), and 5,10-methylenetetrahydrofolic acid and/or an aldehyde of formula (II) are reacted. In the specification and the accompanying drawing, tetrahydrofolic acid may be simply referred to as THF. Similarly, 5,10-methylenetetrahydrofolic acid may be simply referred to as 5,10-methylene THF. 5,10-methylene THF and/or the aldehyde of formula (II) may be used in combination or alone.

Specific examples of R¹ and/or R² may include the following:

Examples of the alkyl group with 1 to 6 carbon atoms may include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a n-pentyl group, an isopentyl group, a neo-pentyl group, a n-hexyl group, and an isohexyl group.

Examples of the aryl group with 6 to 14 carbon atoms may include a phenyl group, a tolyl group, a xylyl group, a biphenyl group, a naphthyl group, an anthryl group, and a phenanthryl group.

Examples of the cycloalkyl group with 3 to 10 carbon atoms may include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptanyl group, a cyclooctanyl group, a cyclononanyl group, and a cyclodecanyl group.

Examples of the aralkyl group with 7 to 19 carbon atoms may include phenylalkyl groups such as a benzyl group, a benzhydryl group, a phenethyl group and a trityl group, a cinnamyl group, a stylyl group, and a naphthylalkyl group.

Examples of the alkoxyalkyl group with 2 to 11 carbon atoms may include an alkyl group with 1 to 10 carbon atoms which has a substituent selected from the group consisting of a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a pentyloxy group, a phenoxy group, a heptoxy group, an octoxy group, a nonanoxy group, and decanoxy group.

R¹ and/or R² may be a group which is identical with any of the aforementioned hydrocarbon groups except for containing a hetero atom in its carbon skeleton. Examples of the hetero atom may include an oxygen atom, a nitrogen atom, and a sulfur atom.

One embodiment of R¹ and/or R² containing the hetero atom in its carbon skeleton may be a heteroring-containing hydrocarbon group. The heteroring-containing hydrocarbon group is a cyclic hydrocarbon group, wherein a ring of the cyclic moiety contains the hetero atom. Examples of the heteroring-containing hydrocarbon group may include heterocyclic groups such as a heteroaryl group with or without aromaticity and may be either monocyclic or polycyclic group. Specific examples of the heteroring-containing hydrocarbon group may include a furyl group, a thienyl group, a pyridyl group, a piperidyl group, a piperidino group, a morpholino group, an indolyl group, an imidazolyl group, and an alkyl group substituted by any of these heterocyclic groups.

R¹ and/or R² may also be a hydrocarbon group which is identical with any of the aforementioned groups except for containing an unsaturated carbon-carbon bond in its carbon skeleton.

In addition, the aforementioned R¹ and/or R² may be linear or branched. Moreover, R¹ and/or R² may be the aforementioned hydrocarbon group which is substituted by the following group or to which the following group is added: one or more groups which include a halogen atom, an alkyl group with up to 3 carbon atoms, an alkoxyl group with up to 3 carbon atoms, a keto group(═O), a hydroxyl group(—OH), a thiol group(—SH), an amino group(—NH₂), an amido group(—CONH₂), an imino group(═NH), and a hydrazino group(—NHNH₂).

Examples of the D-α-amino acid of formula (I) may include alanine, valine, leucine, isoleucine, serine, threonine, cysteine, methionine, asparagine, glutamine, phenylalanine, tyrosine, tryptophan, aspartic acid, glutamic acid, lysine, arginine, histidine, 2-amino-n-butyric acid, all of which are of D-α-type, preferably, alanine, serine, and 2-amino-n-butyric acid, and more preferably, alanine.

Formula (II) does not include formaldehyde (i.e., wherein R² is hydrogen). However, formaldehyde may be used to generate 5,10-methylene THF. 5,10-methylene THF may be easily obtained by reacting formaldehyde with THF. 5,10-methylene THF also reacts with a D-amino acid of formula (I) to produce THF. This means that 5,10-THF and THF may form a cyclic reaction system. According to the method of the present invention, the THF cyclic reaction system may be used as a secondary reaction system.

In formula (III), R¹ is the same as R¹ in formula (I). In formula (III), R³ may be hydrogen, an alkyl group with 1 to 6 carbon atoms, an aryl group with 6 to 14 carbon atoms, a cycloalkyl group with 3 to 10 carbon atoms, an aralkyl group with 7 to 19 carbon atoms, an alkoxyalkyl group with 2 to 11 carbon atoms, a group identical to any of the aforementioned groups except for containing a hetero atom in the carbon skeleton thereof, and a group identical to any of the aforementioned groups except for containing a carbon-carbon unsaturated bond in the carbon skeleton thereof, wherein these groups may be either linear or branched and may have a substituent. Specific examples of the hydrocarbon groups other than hydrogen are the same as those in the aforementioned examples for R¹ and R².

A preferable embodiment of the present invention may be a reaction system in which D-α-alanine reacts with 5,10-methylene THF to produce α-methyl-L-serine. FIG. 1 shows a specific example of the reaction system.

As shown in FIG. 1, THF reacts with formaldehyde to produce 5,10-methylene THF. 5,10-methylene THF is reacted with D-α-alanine in the presence of a predetermined enzyme. Through the reaction, D-α-methyl serine and THF are produced. THF may be reused as a material for supplying 5,10-methylene THF. In the embodiment where formaldehyde is used to reproduce 5,10-methylene THF, it is preferable that a slight amount of formaldehyde is sequentially added to the reaction system. Since formaldehyde has a high reactivity, the sequential addition thereof to keep pace with the consumption of 5,10-methylene THF may result in suppression of by-product production.

Moreover, as shown in the example in FIG. 1, the method of the present invention for producing β-hydroxy amino acid is suitable for preferentially producing the L-isomer of the amino acid when using a predetermined enzyme. The phrase “for preferentially producing the L-isomer” means that the ratio of the L-isomer of the resulting β-hydroxy amino acid is higher than that of the D-amino acid. The ratio of L-isomer is preferably 70% or more, further preferably 80% or more, and still further preferably 90% or more. The ratio of the L-isomer in the serine derivative may be calculated by the expression ([L-isomer]/([D-isomer]+[L-isomer]))*100.

The reaction temperature is preferably 10 to 50° C. and more preferably 20 to 40° C. The pH value for the reaction system is preferably 5 to 9 and more preferably 6 to 8.

According to the method of the present invention, 5,10-methylene THF and/or the aldehyde of formula (II) is reacted with D-α-amino acid in the presence of a predetermined enzyme. The enzyme which catalyzes the reaction may be obtained from a microorganism belonging to genera Paracoccus, Aminobacter, or Ensifer. More specific examples of these microorganisms may include Paracoccus sp., Aminobactor sp., and Ensifer sp. and preferably Paracoccus sp. FERM BP-10604, Aminobactor sp. FERM BP-10605, and Ensifer sp. FERM BP-10606.

The strains having a FERM number assigned are deposited strains as mentioned below and therefore, may be available by referencing to its associated number and the following procedure. These strains were each converted into an International Deposit under the provisions of the Budapest Treaty on May 11, 2006.

(1) Name: Paracoccus sp. AJ110402

Deposit number: FERM BP-10604

Depositary authority: International Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology

Address: Chuoh No. 6, Higashi 1-1-1, Tsukuba, Ibaraki, Japan

Deposit date: Mar. 8, 2005

(2) Name: Aminobactor sp. AJ110403

Deposit number: FERM BP-10605

Depositary authority: International Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology

Address: Chuoh No. 6, Higashi 1-1-1, Tsukuba, Ibaraki, Japan

Deposit date: Mar. 8, 2005

(3) Name: Ensifer. sp. AJ110404

Deposit number: FERM BP-10606

Depositary authority: International Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology

Address: Chuoh No. 6, Higashi 1-1-1, Tsukuba, Ibaraki, Japan

Deposit date: Mar. 8, 2005

More specifically, examples of the enzymes used in the reaction for producing the β-hydroxy amino acid in the present invention may include the following proteins:

(A) a protein having an amino acid sequence of SEQ ID NO: 5;

(B) a variant of the protein having the amino acid sequence of SEQ ID NO: 5, which is able to catalyze the reaction to produce the β-hydroxy amino acid of formula (III);

(C) a protein having an amino acid sequence of SEQ ID NO: 11;

(D) a variant of the protein having the amino acid sequence of SEQ ID NO: 11, which is able to catalyze the reaction to produce the β-hydroxy amino acid of formula (III);

(E) a protein having an amino acid sequence of SEQ ID NO: 16;

(F) a variant of the protein having the amino acid sequence of SEQ ID NO: 16, which is able to catalyze the reaction to produce the β-hydroxy amino acid of formula (III).

The use of any of the aforementioned proteins may achieve efficient production of the β-hydroxy amino acid. According to the method of the present invention, among the β-hydroxy amino acids, the L-amino acid form which has an asymmetric carbon in the α-position may be produced with high selectivity. In particular, in the system where D-α-alanine reacts with 5,10-methylene THF, α-methyl-L-serine only may be substantially produced, which leads to efficient production of the optically-active amino acid.

The protein having the amino acid sequence of SEQ ID NO: 5 may be isolated from the Paracoccus sp. FERM BP-10604 strain. The protein having the amino acid sequence of SEQ ID NO: 11 may be isolated from the Aminobactor sp. BP-10605 strain. The protein having the amino acid sequence of SEQ ID NO: 16 may be isolated from Ensifer sp. FERM BP-10606 strain.

As mentioned above, according to the method of the present invention, proteins which are substantially the same as the proteins (A), (C), and (E), for example, variant proteins, may also be used. For example, protein (B) is a variant of, or substantially the same as, protein (A). A variant protein may have one or more mutations in the amino acid sequence including substitutions, deletions, insertions, additions, and inversions within the sequence. The number of mutations may be one or more, and may vary depending on the position of the amino acid residue to be mutated in the protein structure and type of the amino acid residue, and may be a number which does not substantially affect the protein structure and activity. Specifically, the number of mutations may be 1 to 50, preferably 1 to 30, and more preferably 1 to 10. However, the variant protein (B) may desirably have an activity which is approximately half or more, preferably 80% or more, more preferably 90% or more, and still more preferably 95% or more of the enzyme activity compared with protein (A) under conditions of 30° C., pH6.5 to 8.0.

The mutations in the amino acid sequence of protein variant (B) may be achieved by alternating the nucleotide sequence so that the amino acid at the specific site of the gene encoding the protein is substituted, deleted, inserted, or added using, e.g., the site-specific mutagenic method. Alternatively, the polynucleotide having the nucleotide sequence altered as mentioned above may be obtained through the known conventional mutation process. The mutation process may include an in vitro treatment of the DNA encoding protein (A) with hydroxyamine or the like, and a method in which a microorganism belonging to genus Escherichia which carries DNA encoding protein (A) is treated by means of UV irradiation or with a mutagenic agents commonly used for artificial mutation such as N-methyl-N′-nitro-N-nitrosoguanidine(NTG) and nitrous acid.

The aforementioned mutations may also include naturally-occurring mutations, such as differences between species or between strains of a microorganism. By expressing the DNA having the mutation(s) mentioned above in appropriate cells and examining the enzyme activity of the expressed products, the DNA encoding the protein which is a variant of, or substantially the same protein as, protein (A) may be obtained.

Like the relationship between proteins (A) and (B), protein (D) is an example of a protein variant which is substantially the same as protein (C), and protein (F) is an example of protein variant which is substantially the same as protein (E).

Other examples of protein variants which are substantially the same as proteins (A), (B), and (C) may be proteins which have an amino acid sequence resulting in homology of preferably 70% or more, more preferably 80% or more, and still more preferably 90%, and most preferably 95% or more with respect to proteins (A), (B) and (C). In the present specification, the homology of the amino acid sequence may be obtained by calculating a matching count percentage over the full-length of the polypeptide coded into ORF, using GENETYX software Ver7.0.9 (Genetics) with Unit Size to Compare=2, or by its equivalent calculation method.

The present invention also provides polynucleotides encoding the aforementioned proteins. Due to codon degeneracy, a certain amino acid sequence may be defined by more than one nucleotide sequence. That is, the polynucleotide of the present invention includes polynucleotides having nucleotide sequences which encode any of the aforementioned proteins (A), (B), (C), (D), (E), and (F).

Specifically, examples of the polynucleotide of the present invention may include the following polynucleotides:

(a) a polynucleotide having a nucleotide sequence of SEQ ID NO: 4;

(c) a polynucleotide having a nucleotide sequence of SEQ ID NO: 10; and

(e) a polynucleotide having a nucleotide sequence of SEQ ID NO: 15.

The polynucleotide of (a) encodes the protein (A), and may be isolated from the Paracoccus sp. FERM BP-10604 strain. The polynucleotide (c) encodes the protein (C), and may be isolated from the Aminobacter sp. FERM BP-10605 strain. The polynucleotide (e) encodes the protein (E), and may be isolated from the Ensifer sp. FERM BP-10606 strain.

Taking the polynucleotide (a) as an example, a method for isolating the polynucleotides will be described. The DNA having the nucleotide sequence of SEQ ID NO: 4 may be obtained from a chromosomal DNA of Paracoccus sp. or a DNA library by PCR (polymerase chain reaction, see White, T. J. et al; Trends Genet., 5, 185 (1989)) or hybridization. The primer used for PCR may be designed based on, for example, the internal amino acid sequence of a purified protein which is able to catalyze the reaction involved in the method of the present invention. Alternatively, the primer or the probe for hybridization may be designed based on the nucleotide sequence of SEQ ID NO: 4, and the DNA may be isolated using the probe. A combination of a primer having a sequence corresponding to a 5′ non-translation domain and another primer having a sequence corresponding to 3′ non-translation domain, between which lies a coding domain, may be used for the primer for PCR to amplify the full-length of the protein coding domain.

The primer may be synthesized in the usual manner, for example, by the phosphoramidite method (see Tetrahedron Letters (1981), 22, 1859) using DNA synthesizing equipment Model 380B (Applied Biosystems). The PCR process may be performed using, for example, Gene Amp PCR System 9600 (PERKIN ELMER) and TaKaRa LA PCR in vitro Cloning Kit (TaKaRa Bio) according to the method specified by the manufacturer.

The polynucleotides which are substantially the same as the aforementioned polynucleotides (a), (c), and (e) are also included in the polynucleotide of the present invention. The polynucleotides (b), (d) and (f) described below may be enumerated as examples of the polynucleotide which are substantially the same as the polynucleotides (a), (c) and (e), respectively.

Polynucleotide (b) is able to hybridize with a nucleotide sequence complementary to that of SEQ ID NO: 4 under stringent conditions, and encodes a protein which is able to catalyze the reaction of a D-α-amino acid of formula (I) with 5,10-methylene THF and/or an aldehyde of formula (II) to produce β-hydroxy amino acid of formula (III);

Polynucleotide (d) is able to hybridize with a nucleotide sequence complementary to that of SEQ ID NO: 10 under stringent conditions, and encodes a protein which is able to catalyze the reaction of a D-α-amino acid of formula (I) with 5,10-methylene THF and/or an aldehyde of formula (II) to produce β-hydroxy amino acid of formula (III);

Polynucleotide (f) is able to hybridize with a nucleotide sequence complementary to that of SEQ ID NO: 15 under stringent conditions, and encodes a protein which is able to catalyze the reaction of a D-α-amino acid of formula (I) with 5,10-methylene THF and/or an aldehyde of formula (II) to produce β-hydroxy amino acid of formula (III).

For the polynucleotide to be hybridized, a probe, for example, may be used. In each case, the probe may be prepared in the usual manner based on the nucleotide sequences of SEQ ID Nos. 4, 10, and 15. The objective polynucleotide may be isolated by picking out the nucleotide to be hybridized using the probe in the usual manner. The DNA probe, for example, may be prepared by amplifying the nucleotide sequences cloned into plasmid or a phage vector, cutting out the desired nucleotide sequence for the probe by a restriction enzyme, and then extracting the sequence. The portion to be cut out may be adjusted according to the objective DNA. Once the polynucleotide which is substantially the same has been detected, the polynucleotide may be amplified in the usual manner such as PCR.

The “stringent conditions” mean conditions under which a so-called specific hybrid is formed but a nonspecific hybrid is not formed. Although it is difficult to clearly define the condition in terms of numerical values, an example of such conditions may be those under which the DNAs having high homology, for example, 50% or more, preferably 70% or more, more preferably 80% or more, further preferably 90% or more, and still further preferably 95% or more, are hybridized while the DNAs having lower homology are not hybridized. The homology (%) of the nucleotide sequences is represented by numeric values obtained by percentage calculation over the full-length of ORF of each gene (including a stop codon) using GENETYX software Ver7.0.9 (Genetics) with Unit Size to Compare=6, pick up location=1. As another example, stringent conditions may be those of ordinary washing conditions in Southern hybridization, under which the DNAs are hybridized at 60° C. and salt concentration of 1×SSC, 0.1% SDS, and preferably 0.1×SSC, 0.1% SDS. The genes hybridized under such conditions may include a gene containing a stop codon or a gene without activity due to a mutation in the activity center region. However, these may be easily screened off by inserting the obtained genes in a commercially-available expression vector, expressing the genes in an appropriate host, and determining the enzyme activity of the expressed product by a method described later.

As mentioned above, in the case of the aforementioned polynucleotide (b), the protein encoded thereby may desirably have an activity of approximately half or more, preferably 80% or more, and more preferably 90% or more of the activity of protein (A), which is encoded by the nucleotide sequence of SEQ ID NO: 4 under conditions of 30° C., pH8.0. Similarly, in the case of the aforementioned polynucleotide (d), the protein encoded thereby may desirably have the activity to the same extent as the above with respect to the protein (C). In the case of the aforementioned polynucleotide (f), the protein encoded thereby may desirably have the activity to the same extent as the above with respect to the protein (E).

According to the method of the present invention, the enzyme may be used in any form as long as it is capable of catalyzing the aforementioned reaction in the reaction system. Examples of the specific forms thereof may include a cultured product of enzyme-producing microorganism, cells of the microorganism separated from the cultured product, and a processed cell product. The cultured product of the microorganism is a product obtained by culturing the microorganism. More specifically, the cultured product is a mixture containing the cells of the microorganisms, the cultivation medium used for culturing the microorganism, and the substances produced by the cultured microorganism. The cells of the microorganisms may be washed before using as the washed cells. The processed cell product may be disrupted, lysed, and/or freeze-dried cells, as well as a crude-purified protein that is collected from the processed cells, and a purified protein that is further purified. As for the purified proteins, a partially-purified protein which is obtained by a variety of types of purification methods may be used. Alternatively, a fixed protein which is fixed by a covalent bond method, an adsorption method, or an entrapment method may be used. Depending on the employed microorganism, a part of the cells may be lysed during cultivation. In this case, the supernatant of the cultivation medium may also be used as an enzyme-containing substance.

Now, the method for producing the proteins of the present invention and the method for preparing the recombinants and transformants used in producing the proteins will be described hereinbelow using the aforementioned protein (A) as an example. The methods which will be described below are also applicable to other proteins.

The transformant which expresses the aforementioned protein (A) may be prepared using a recombinant polynucleotide which contains the polynucleotide having the aforementioned nucleotide sequence (a) incorporated therein. For example, the transformant may be obtained by preparing a recombinant DNA containing the DNA having the nucleotide sequence of SEQ ID NO: 4, and then introducing the resulting recombinant DNA into an appropriate host. Examples of the host for expressing the protein identified by the DNA having the nucleotide sequence of SEQ ID NO: 4 may include a variety of prokaryotic cells, including microorganisms belonging to genus Escherichia such as Escherichia coli, microorganisms belonging to genus Corynebacterium, Bacillus subtilis, and a variety of eukaryotic cells including Saccharomyces cerevisiae, Pichia stipitis, and Aspergillus oryzae. Using the host which may be easily handled without any expensive components upon cultivation, β-hydroxy amino acid may be easily produced on a large scale.

The recombinant DNA for introducing the DNA having the nucleotide sequence of SEQ ID NO: 4 into a host may be prepared by inserting the DNA into a vector suitable for the type of the host so that the inserted DNA can express the protein encoded thereby. If the promoter inherently exists with the gene encoding the aforementioned enzyme derived or isolated from, e.g., Paracoccus sp., Aminobacter sp., and Ensifer sp. are capable of functioning in the host cells, such a promoter may be used as the promoter for facilitating the expression of the proteins. Alternatively, if necessary, any other promoter which can function in the host may be coupled to the DNA of SEQ ID NO: 4 or the like so that the proteins are expressed under the control of the promoter.

Examples of methods for transforming the recombinant DNA to introduce the recombinant DNA into the host cell may include the D. M. Morrison's method (Methods in Enzymology 68, 326 (1979)) and a method for improving the permeability of the DNA by treating a recipient cell with calcium chloride (Mandel, M. and Higa, A., J. Mol. Biol., 53, 159 (1970)).

In the case of producing an objective protein on a large scale using the recombinant DNA technology, one of the preferable embodiments may be the formation of an inclusion body of the protein. The inclusion body is configured by aggregation of the protein in the protein-producing transformant. The advantages of this expression production method may be protection of the objective protein from digestion due to protease in the microbial cells, and ready purification of the objective protein that may be performed by disruption of the microbial cells and following centrifugation. To obtain the active protein from the protein inclusion body, a series of manipulations such as solubilization and activity regeneration is required, and thus, the manipulations are more complicated than those used when directly producing the active protein. However, when a protein which affects microbial cell growth is produced on a large scale in the microbial cells, effects thereof may be avoided by accumulating the protein as an inactive inclusion body in the microbial cells.

Examples of the methods for producing the objective protein on a large scale as an inclusion body may include methods of expressing the protein alone under the control of a strong promoter, as well as methods of expressing the objective protein as a fusion protein with a protein known to be expressed in a large amount.

As the host to be transformed, any strain commonly used in expressing heterogenes may be used. Suitable examples thereof may include the Escherichia coli JM109, DH5α, HB101, and BL21 strains, which are subspecies of the Escherichia coli K12 strain. The method for transforming the host and the method for selecting out the transformants are described in Molecular Cloning: A Laboratory Manual, 3rd edition, Cold Spring Harbor press (2001 Jan. 15). An example of the method for preparing the transformed Escherichia coli strain and producing a predetermined enzyme using the transformed strain will be specifically described hereinbelow.

As the promoter for expressing the DNA encoding the mutant protein, the promoters typically used for producing xenogenic proteins in E. coli may be used, and examples thereof may include strong promoters such as T7 promoter, lac promoter, trp promoter, trc promoter, tac promoter, and PR promoter and PL promoter of lambda phage. As the vector, pUC19, pUC18, pBR322, pHSG299, pHSG298, pHSG399, pHSG398, RSF1010, pMW119, pMW118, pMW219, pMW218, pACYC177, pACYC184, and derivatives thereof may be used. Other vectors of phage DNA may also be used. In addition, expression vectors which contain a promoter and can express the inserted DNA sequence may also be used.

In order to produce the mutant protein as a fusion protein inclusion body, a fusion protein gene is produced by linking a gene encoding another protein, preferably a hydrophilic peptide, upstream or downstream of the mutant protein gene. Such a gene encoding another protein may be those which increase the amount of the accumulated fusion protein and enhance solubility of the fusion protein after denaturation and regeneration steps. Examples of candidates thereof may include T7 gene 10, β-galactosidase gene, dehydrofolic acid reductase gene, interferon γ gene, interleukin-2 gene and prochymosin gene.

Such a gene may be ligated to the gene encoding the mutant protein so that reading frames of codons are matched. This may be effected by ligating at an appropriate restriction enzyme site or using a synthetic DNA having an appropriate sequence.

In some cases, it is preferable to ligate a terminator, i.e. the transcription termination sequence, downstream of the fusion protein in order to increase the production amount. Examples of this terminator may include T7 terminator, fd phage terminator, T4 terminator, tetracycline resistant gene terminator, and E. coli trpA gene terminator.

The vector for introducing the gene encoding the mutant protein or the fusion protein of the mutant protein with the other protein into E. coli may preferably be of a so-called multicopy type. Examples thereof may include plasmids having a replication origin derived from ColE1, such as pUC based plasmids, pBR322 based plasmids or derivatives thereof. As used herein, the “derivative” means the plasmid modified by the substitution, deletion, insertion, addition and/or inversion of the nucleotides. “Modified” referred to herein includes the modification by mutagenesis with the mutagen or UV irradiation and natural mutation.

In order to select the transformants, it is preferable to employ a vector having a marker such as an ampicillin resistant gene. As such a plasmid, expression vectors having the strong promoter are commercially available (pUC series: Takara Shuzo Co., Ltd., pPROK series and pKK233-2: Clontech, etc.).

A DNA fragment where the promoter, the gene encoding the protein having the objective activity or the fusion protein of the objective protein with the other protein, and in some cases the terminator are ligated sequentially, is then ligated to the vector DNA to obtain a recombinant DNA.

The resulting recombinant DNA is used to transform Escherichia coli and then the transformed Escherichia coli is cultured, to express and produce the predetermined protein or its fused protein.

In the case of expressing the fusion protein, the fusion protein may be composed so as to be able to cleave out the objective enzyme therefrom using a restriction protease which recognizes a sequence of blood coagulation factor Xa, kallikrein or the like which is not present in the objective enzyme.

As production media, media such as M9-casamino acid medium and LB medium which are typically used for cultivation of E. coli may be used. The conditions for cultivation and a production induction may be appropriately selected depending on types of the marker and the promoter of the vector and the host used.

The following methods are available for recovering the objective protein or the fusion protein containing the objective protein with the other protein. If the objective protein or the fusion protein thereof is solubilized in the microbial cells, the cells may be collected and then disrupted or lysed to thereby obtain a crude enzyme solution for use. If necessary, the crude solution may be purified using techniques such as ordinary precipitation, filtration and column chromatography, to obtain the purified objective protein or the fusion protein. In this case, the purification may be performed using an antibody against the mutant protein or the fusion protein. In the case where the protein inclusion body is formed, it may be solubilized with a denaturant, and then the denaturant may be removed by means of dialysis or the like to obtain the objective protein.

EXAMPLES

The present invention will be described in more detail with reference to the following non-limiting examples.

Example 1 Detection of 2-methylserine Hydroxylmethyl Transferase Activity

In a nutrient broth agar medium (Difco), microorganisms listed in Table 1 were cultured at 30° C. for 24 hours. A platinum loopful of the resulting cells were inoculated into 3 ml of nutrient broth liquid medium and then cultured at 30° C. for 24 hours, with 120 reciprocations/minute. 0.15 ml of the resulting cultured solution was inoculated into 3 ml of nutrient broth liquid medium containing 0.2% α-methyl-DL-serine and cultured at 30° C. for 24 hours with 120 reciprocations/minute.

After cultivation, the cells were centrifuged and then washed twice with an equal volume of 50 mM potassium phosphate buffer (pH7.4) containing 0.1 mM pyridoxal phosphoric acid. 50 M potassium phosphate buffer (pH7.4) containing 0.1 mM pyridoxal phosphoric acid was used to prepare a total amount (0.3 ml) of cell suspension and then the suspension was ultrasonically disrupted at 4° C. The supernatant obtained by centrifugation (16,000 g, 10 min.) was dialyzed with 50 mM potassium phosphate buffer (pH7.4) containing 0.1 mM pyridoxal phosphoric acid to obtain a cell-free extracted solution.

0.05 ml of cell-free extracted solution was added to a reaction solution (1), which has a composition of 50 mM potassium phosphate buffer (pH7.4), 10 mM α-methyl-DL-serine, 0.5 mM tetrahydrofolic acid, 10 mM 2-mercaptoethanol, 0.01 mM pyridoxal phosphoric acid, 10 mM sodium ascorbate, 0.4 mM NADP, and 1 U/ml 5,10-methylene tetrahydrofolic acid dehydrogenase. The total amount (0.1 ml) of solution was reacted at 30° C. for 10 minutes. The reaction was stopped with 0.15 ml of 0.6 N hydrochloric acid. The supernatant obtained by centrifugation (16,000 g, 10 minutes) was left to stand at room temperature for 10 minutes. Absorbance (E11) of the supernatant caused by 5,10-methenyl-5,6,7,8-tetrahydrofolic acid was measured at 350 nm. As a control, another reaction was performed in the same way as the above, except that α-methyl-DL-serine was replaced with water in the aforementioned solution (1), and the absorbance (E10) caused by 5,10-methenyl-5,6,7,8-tetrahydrofolic acid in the resulting liquid was measured. Based on the measured absorbance, the alteration in the absorbance specific to α-methyl-DL-serine (EΔ1=E11-E10) was calculated. The results are shown in Table 1.

TABLE 1 Strain EΔ1 Paracoccus 1.35 sp. A13 Aminobacter 2.07 sp. A10 Ensifer sp. 1.25 B30

Example 2 Purification of 2-methyl Serine Hydroxylmethyl Transferase Derived from the Paracoccus sp. AJ110402 Strain

(1) Preparation of Cell-free Extracted Solution

Cells of Paracoccus species were cultured in the nutrient broth agar medium (Difco) at 30° C. for 24 hours. The cultured cells were inoculated into 50 ml of nutrient broth liquid medium in a 500 ml Sakaguchi flask and cultured at 30° C. for 24 hours with 120 reciprocations/minute. The resulting cultured solution was inoculated into 2 L of liquid medium containing 0.2% α-methyl-DL-serine, and 0.17% yeast nitrogen base w/o amino acid and ammonium sulfate (pH7.0). 50 ml each of the mixture was dispensed into each of the 500 ml Sakaguchi flasks, and then cultured at 30° C. for 22 hours with 120 reciprocations/minute. The resulting cells were collected by centrifugation (8,000 g, 10 minutes) and washed twice with 25 mM potassium phosphate buffer containing 0.02 mM pyridoxal phosphoric acid (referred to hereinafter as the buffer (I)). Then, 100 ml of cell suspension was prepared using the buffer (I). The cells were ultrasonically disrupted and centrifuged (18,000 g, 10 minutes), and the resulting supernatant was ultra-centrifuged (200,000 g, 30 minutes). The resulting supernatant was used as the cell-free extracted solution.

(2) Anion-exchange Chromatography

The cell-free extracted solution was applied to a ResourceQ column (Amersham Biosciences) which had been previously equilibrated with the buffer (I), and the enzyme was eluted by a linear concentration gradient of 0-1M sodium chloride. This process was conducted twice by dividing the cell-free extracted solution into two aliquots.

(3) Hydrophobic Interaction Chromatography

Active fractions of the enzyme obtained in the aforementioned (2) were mixed with the buffer (I) containing an equivalent amount of 2M ammonium sulfate and then applied to the Phenyl-Sepharose column (Amasham Biosciences) which had been previously equilibrated with the buffer (I) containing 1M ammonium sulfate. Then, the enzyme was eluted by the linear concentration gradient of 1-0M ammonium sulfate.

(4) Hydroxyapatite Column Chromatography

The active fractions obtained in the aforementioned (3) were dialyzed with the 2.5 mM potassium phosphate buffer (pH6.8) containing 0.02 mM pyridoxal phosphoric acid and then applied to the CellulofineHAp columns (SEIKAGAKU Corp.) which had been previously equilibrated with the same buffer. The enzyme was eluted with the 2.5-250 mM potassium phosphate buffer (pH6.8). The active fractions of the enzyme were used as the purified enzyme in the following experiments.

The enzyme thus obtained in this way had specific activity of 3.51 U/mg. The enzyme was electrophoresed in SDS-polyacrylamide and the gel was stained with a Coomassie brilliant blue staining fluid. A homogeneous band appeared at a position of the molecular weight of approximately 47,000.

Example 3 Determination of the Amino Acid Sequence of 2-methyl Serine hydroxylmethyl transferase Derived From the Paracoccus sp. AJ110402 Strain and the Nucleotide Sequence Encoding the Same

50 pmol of the purified enzyme which had been prepared in Example 2 was electrophoresed in SDS-polyacrylamide, and transferred on a PVDF membrane. The relevant part was put in a protein sequencer to determine 30 amino acids (SEQ ID NO: 1).

Subsequently, 5 μg of genome DNA derived from the Paracoccus sp. AJ110402 strain was cleaved with PstI (50 U) and then ligated to the PstI cassette of TaKaRa LA PCR in vitro Cloning Kit in accordance with the kit directions. Using the ligated mixture as a template, PCR (94° C.: 30 sec., 47° C.: 2 min., 72° C.: 1 min., 30 cycles) was performed with a cassette primer C1 and a primer HMT_FW1 (SEQ ID NO: 2). Using the PCR reaction solution as a template, the second PCR (94° C.: 30 sec., 55° C.: 2 min., 72° C.: 1 min., 30 cycles) was performed with a cassette primer C2 and a primer HMT_FW2 (SEQ ID NO: 3). Approximately 0.7 kb-length fragments, of which amplification had been confirmed, were ligated to pGEM-Teasy (Promega), with which Escherichia coli JM109 strain was then transformed. The nucleotide sequence of the plasmid having the objective fragment was confirmed with a DNA sequencer (ABI3100). Approximately 1.1 kb-length gene fragment was obtained by treating the plasmid with EcoRI/PstI. Using the fragment as a probe, chromosomal DNAs were subjected to Southern analysis after treatment with various types of restriction enzymes. When the treatment was performed with BglII/NruI, a positive signal was confirmed in an approximately 3.5 kb region.

Subsequently, the chromosomal DNAs were treated with BglII/NruI and then electrophoresed in an agarose gel, to purify the approximately 3.5 kb fragment. The fragment was then ligated to the pUC19 BamHI/SmaI site. Using this reaction solution, Escherichia coli JM109 was transformed to create a library. The aforementioned probe was used to perform colony hybridization for obtaining positive colonies. A plasmid was extracted from the positive colonies. The plasmid was designated pHMT01. As to the inserted 3475 bp part, the nucleotide sequence thereof was determined. As a result, an ORF (SEQ ID NO: 4) composed of 425 amino acids was found. The ORF had the same sequence as the amino acid sequence obtained from N-terminal analysis, which confirms that the objective gene was obtained. As for the ORF of the gene sequence, a homology search was conducted. As a result, 55% homology was confirmed between serine hydroxylmethyl transferase derived from Methylobacterium extorquens and the ORF amino acid sequence.

Example 4 Expression of 2-methylserine Hydroxylmethyl Transferase Gene Derived from the Paracoccus sp. AJ110402 Strain in Escherichia coli

Using pHMT01 as a template, PCR was performed with a primer PHMT_SD_Eco (SEQ ID NO: 6) and a primer PHMT_ter2_Hind (SEQ ID NO: 7) to amplify a 1.2 kb region of 2-methylserine hydroxylmethyl transferase. The amplified sequence was treated with EcoRI/HindIII, and then ligated to pUC18 which had been previously treated with EcoRI/HindIII. With the ligated product, Escherichia coli JM109 strain was transformed. A transformant having plasmid (pUCPHMT01) containing the objective gene fragment was thus obtained. The transformant was designated JM109/pUCPHMT01.

JM109/pUCPHMT01 was pre-cultured in the LB medium containing 100 mg/L ampicillin at 37° C. for 16 hours. 2.5 ml of the pre-cultured solution was inoculated into 50 ml of the LB medium containing 100 mg/L ampicillin and cultured at 37° C. One hour after the onset of the cultivation, IPTG was added so that the final concentration thereof reached 1 mM. The mixture was further cultured for four hours. The resulting cells were collected by centrifugation and washed with the 50 mM phosphoric acid buffer (pH7.4) containing 0.1 mM pyridoxal phosphoric acid. A cell suspension was then prepared using the same buffer. The cells were ultrasonically disrupted and centrifuged (18,000 g, 10 min., 4° C.) to obtain a supernatant. 2-methylserine hydroxylmethyl transferase activity was measured as to the supernatant as the cell-free extracted solution. The measured value was 3.02 U/mg. Apart from the above, pUC18 was introduced into JM109 strain to obtain a transformant JM109/pUC18, and a cell-free extracted solution was prepared therefrom and the activity was measured in the same manner as described above. The measured activity was less than the detection limit.

Example 5 Isolating the 2-methylserine Hydroxylmethyl Transferase Gene from the Aminobactor sp. AJ110403 Strain

Using the genomic DNA prepared from the Aminobactor sp. AJ110403 strain as a template, PCR was performed with mixed primers HMT_MIX_FW1 (SEQ ID NO: 8) and HMT_MIX_RV2 (SEQ ID NO: 9). An amplified fragment of 0.6 kb was confirmed. Using this PCR product as a probe, the genome DNA of the Aminobactor sp. AJ110403 strain was subjected to BamHI treatment and Southern analysis. As a result, a positive signal appeared in a 3.5 kb-length region.

Subsequently, the genomic DNA of the Aminobactor sp. AJ110403 strain was treated with BamHI and electrophoresed in the agarose gel. A fragment of approximately 3.5 kb was purified. The fragment was ligated to the pUC118 BamHI site. Using this reaction solution, Escherichia coli JM109 was transformed to create a library. The aforementioned probe was used to perform colony hybridization for obtaining positive colonies, and a plasmid was extracted from the positive colonies. The plasmid was designated pAHMT01. As for the inserted part in the plasmid, the nucleotide sequence thereof was determined. As a result, existence of an ORF composed of 425 amino acids was confirmed (SEQ ID NO: 10).

Using pAHMT01 as a template, PCR was performed with primers A2_Bam (SEQ ID NO: 12) and A2_ter_Pst (SEQ ID NO: 13). The amplified fragment of 1.2 kb obtained by PCR was treated with BamHI/PstI, and then inserted into pUC18 BamHI/PstI site, to obtain pUCAHMT01. Using this plasmid, Escherichia coli JM109 was transformed. The transformant was designated JM109/pUCAHMT01.

JM109/pUCAHMT01 was pre-cultured in the LB medium containing 100 mg/L ampicillin at 37° C. for 16 hours. 2.5 ml of pre-cultured solution was inoculated into 50 ml of the LB medium containing 100 mg/L ampicillin and cultured at 37° C. One hour after the onset of the cultivation, IPTG was added so that the final concentration thereof reached 1 mM. The mixture was further cultured for four hours. The resulting cells were collected by centrifugation and washed with the 50 mM phosphoric acid buffer (pH7.4) containing 0.1 mM pyridoxal phosphoric acid. A cell suspension was then prepared using the same buffer. The cells were ultrasonically disrupted and centrifuged (18,000 g, 10 min., 4° C.) to obtain a supernatant. 2-methylserine hydroxylmethyl transferase activity was measured as to the supernatant as the cell-free extracted solution. The measured value was 0.27 U/mg. The activity as to the cell-free extracted solution prepared from JM109/pUC18 in the same manner as described above was less than the detection limit.

Example 6 Isolating 2-methylserine Hydroxylmethyl Transferase Gene from the Ensifer sp. AJ110404 Strain

Using genomic DNA prepared from the Ensifer sp. AJ110404 strain as a template, PCR was performed with mix primers HMT_MIX_FW2 (SEQ ID NO: 14) and HMT_MIX_RV2 (SEQ ID NO: 9). An amplified fragment of 0.6 kb was confirmed. Using this PCR product as a probe, the genomic DNA from the Ensifer sp. AJ strain was subjected to EcoRI treatment and Southern analysis. As a result, a positive signal appeared in a 5 kb-length region.

Subsequently, genomic DNA from the Ensifer sp. AJ110404 strain was treated with EcoRI and electrophoresed in the agarose gel. A fragment of approximately 5 kb was purified. The fragment was ligated to the pUC118 EcoRI site. Using this reaction solution, Escherichia coli JM109 was transformed to create a library. The aforementioned probe was used to perform colony hybridization for obtaining positive colonies, and a plasmid was extracted from the positive colonies. The plasmid was designated pEHMT01. As to the inserted part in the plasmid, the nucleotide sequence thereof was determined. As a result, existence of an ORF composed of 425 amino acids was confirmed (SEQ ID NO: 15).

Using pEHMT01 as a template, PCR was performed with primers B_Eco (SEQ ID NO: 17) and B_ter_Bam (SEQ ID NO: 18). The amplified fragment of 1.2 kb obtained by PCR was treated with BamHI/EcoRI, and then inserted into pUC18 BamHI/EcoRI site, to obtain pUCEHMT01. Using this plasmid, Escherichia coli JM109 was transformed. The transformant was designated JM109/pUCEHMT01.

JM109/pUCEHMT01 was pre-cultured in the LB medium containing 100 mg/L ampicillin at 37° C. for 16 hours. 2.5 ml of pre-cultured solution was inoculated into 50 ml of the LB medium containing 100 mg/L ampicillin and cultured at 37° C. One hour after the onset of the cultivation, IPTG was added so that the final concentration thereof reached 1 mM. The mixture was further cultured for four hours. The resulting cells were collected by centrifugation and washed with the 50 mM phosphoric acid buffer (pH7.4) containing 0.1 mM pyridoxal phosphoric acid. A cell suspension was then prepared using the same buffer. The cells were ultrasonically disrupted and centrifuged (18,000 g, 10 min., 4° C.) to obtain a supernatant. 2-methylserine hydroxylmethyl transferase activity was measured as to the supernatant as the cell-free extracted solution. The measured value was 0.10 U/mg. The activity as to the cell-free extracted solution prepared from JM109/pUC18 in the same manner as described above was less than the detection limit.

Example 7 Production of α-methyl-L-serine with 2-methylserine hydroxylmethyl transferase Isolated from Paracoccus sp. AJ110402

The purified enzyme solution which was prepared in Example 2 was added to a composition composed of 100 mM D-alanine, 20 mM formaldehyde, 0.5 mM tetrahydrofolic acid, 10 mM sodium ascorbate, 10 mM 2-mercaptoethanol, 0.1 mM pyridoxal phosphoric acid, and 50 mM phosphoric acid buffer (pH7.4), so that the final concentration of the enzyme reached 47 μg/ml. The reaction was performed at 30° C. for 16 hours. As formaldehyde, the highest quality formaldehyde liquid [code No.: 16223-55] from Nakarai Tesque was used.

After the reaction, an equivalent amount of 2 mM aqueous copper sulfate was added thereto and HPLC was performed using Sumichiral OA-6100 (Sumika Chemical Analysis Service, Ltd.)(mobile phase: 1 mM aqueous copper sulfate, column temperature: 40° C., flow rate: 1 ml/min., detection: UV215 nm). As a result, 19 mM of α-methyl-L-serine was detected but no peak attributed to α-methyl-D-serine was detected.

Example 8 Production of α-methyl-L-serine with Escherichia coli Expressing the 2-methylserine hydroxylmethyl transferase Gene Isolated from Paracoccus sp. AJ110402

Using the method described in Example 4, 400 ml of the cultured liquid of JM109/pUCPHMT01 was prepared. After centrifugation, the cells were washed with 50 mM phosphoric acid buffer (pH8.0) containing 0.1 mM pyridoxal phosphoric acid. The cells were added to the 100 ml of reaction solution (150 mM (15 mmol) D-alanine, 0.1 mM pyridoxal phosphoric acid, 0.3 mM tetrahydrofolic acid, 10 mM 2-mercaptoethanol, 20 mM phosphoric acid buffer (pH8.0)) and then 50.5 ml of 600 mM aqueous formaldehyde was added thereto over 24 hours at 30° C. while stirring. As formaldehyde, the highest quality formaldehyde liquid from Nakarai Tesque [code number: 16223-55] was used.

Under the same conditions as those in Example 7, HPLC analysis was performed. As a result, 66.4 mM (9.5 mmol) of α-methyl-L-serine was detected in the reaction solution but the amount of α-methyl-D-serine production was less than the detection limit.

Example 9 Homology of Proteins

Homology was examined for the amino acid sequences of the enzymes obtained in the aforementioned examples. In calculating the homology of the amino acid sequences, Marching count percentage was calculated over the full-length of the polypeptide chain encoded in ORF using GENETYX software Ver7.0.9 (Genetics) with Unit Size to Compare=2.

Amino acid sequences of the following enzymes derived from Methylobacterium Extorquens have been deposited as accession No. AAA64456 in GenBank (National Center for Biotechnology Information). Amino acid sequences of the following enzymes derived from Escherichia coli have been deposited as accession No. AAA23912 in GenBank.

TABLE 2 Paracoccus Aminobacter sp. sp. Ensifer sp. SEQ ID SEQ ID NO: SEQ ID NO: Methylobacterium NO: 5 11 16 Extorquens E. coli Paracoccus sp. 100 84.7 80.0 55.5 50.4 SEQ ID NO: 5 Example EC 2.1.2.7 Aminobacter sp. 100 82.8 56.1 51.9 SEQ ID NO: 11 Example EC 2.1.2.7 Ensifer sp. 100 55.8 49.3 SEQ ID NO: 16 Example EC 2.1.2.7 Methylobacterium 100 59.8 Extorquens Comparative example EC 2.1.2.1 E. coli 100 Comparative example EC 2.1.2.1

INDUSTRIAL APPLICABILITY

The method of the present invention is useful in the industries involving in amino acid production. It is expected that the present invention will contribute to the production of various types of β-hydroxy amino acid and optically-active amino acid, and specifically, the method may be used in producing, for example, intermediates for pharmaceuticals.

Although the present invention has been described with reference to the preferred examples, it should be understood that various modifications and variations can be easily made by those skilled in the art without departing from the spirit of the invention. Accordingly, the foregoing disclosure should be interpreted as illustrative only and is not to be interpreted in a limiting sense. The present invention is limited only by the scope of the following claims along with their full scope of equivalents. Each of the aforementioned documents, including the foreign priority document, is incorporated by reference herein in its entirety. 

1. A method for producing β-hydroxy amino acid of formula (III):

comprising reacting a D-α-amino acid of formula (I):

with 5,10-methylenetetrahydrofolic acid in the presence of formaldehyde and a protein selected from the group consisting of: (A) a protein comprising the amino acid sequence of SEQ ID NO: 5; (B) a variant protein of the amino acid sequence of SEQ ID NO: 5 which is at least 95% homologous to the amino acid sequence of SEQ ID NO. 5, and which is able to catalyze the reaction to produce the β-hydroxy amino acid of formula (III); and wherein R¹ is selected from the group consisting of an alkyl group with 1 to 6 carbon atoms, wherein R¹ may be either linear or branched, and may have one or more substituents selected from the group consisting of a halogen atom, an alkyl group with up to 3 carbon atoms, an alkoxyl group with up to 3 carbon atoms, a keto group, a hydroxyl group, a thiol group, an amino group, an amido group, an imino group, and a hydrazine group and wherein R³ is hydrogen.
 2. The method for producing the β-hydroxy amino acid according to claim 1, wherein said D-α-amino acid is D-α-alanine and said β-hydroxy amino acid is α-methyl-L-serine.
 3. The method of claim 1, wherein said protein comprising the amino acid sequence of SEQ ID NO.: 5, or said variant protein thereof, is a product of a transformant containing a recombinant polynucleotide comprising a polynucleotide encoding said protein.
 4. The method of claim 3, wherein said polynucleotide is selected from the group consisting of: (a) the polynucleotide comprising the nucleotide sequence of SEQ ID NO.: 4; (b) a polynucleotide which hybridizes with the nucleotide sequence complementary to that of SEQ ID NO: 4 under stringent conditions wherein the stringent conditions are 60° C., 1×SSC and 0.1% SDS.
 5. The method for producing the β-hydroxy amino acid according to claim 1, wherein said protein is (A) a protein comprising the amino acid sequence of SEQ ID NO:
 5. 6. The method for producing the β-hydroxy amino acid according to claim 2, wherein said protein is (A) a protein comprising the amino acid sequence of SEQ ID NO:
 5. 7. The method for producing the β-hydroxy amino acid according to claim 3, wherein said D-α-amino acid is D-α-alanine and said β-hydroxy amino acid is α-methyl-L-serine.
 8. The method for producing the β-hydroxy amino acid according to claim 3, wherein said protein is (A) a protein comprising the amino acid sequence of SEQ ID NO:
 5. 9. The method for producing the β-hydroxy amino acid according to claim 7, wherein said protein is (A) a protein comprising the amino acid sequence of SEQ ID NO:
 5. 10. The method for producing the β-hydroxy amino acid according to claim 4, wherein said D-α-amino acid is D-α-alanine and said β-hydroxy amino acid is α-methyl-L-serine.
 11. The method for producing the β-hydroxy amino acid according to claim 4, wherein said protein is (A) a protein comprising the amino acid sequence of SEQ ID NO:
 5. 12. The method for producing the β-hydroxy amino acid according to claim 10, wherein said protein is (A) a protein comprising the amino acid sequence of SEQ ID NO:
 5. 13. The method for producing β-hydroxy amino acid according to claim 1, wherein R¹ is methyl or ethyl.
 14. The method for producing β-hydroxy amino acid according to claim 13, wherein said protein comprises the amino acid sequence of SEQ ID NO.:
 5. 